Annealing effects on nitrogen site ordering and anisotropic magnetoresistance in pseudo-single-crystal γ′-Fe₄N films

Pseudo-single-crystal γ ′-Fe₄N films were fabricated by changing the degree of order (S) of N sites, and their anisotropic magnetoresistance (AMR) effects along the Fe₄N[100] direction were investigated. Negative AMR ratios were observed in all the specimens in the temperature range of 5-300 K. Specific features-a marked increase in the AMR magnitude below 50K and the appearance of the cos 4θ term in the AMR curve below 30K-were clearly observed in the case of high S, and these features decreased with decreasing S. The physical origin of these features is proposed to be a crystal field effect on the AMR.